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Understanding the Cyclic (In)stability and the Effects of Presence of a Stable Conducting Network on the Electrochemical Performances of Na 2 Ti 3 O 7
Author(s) -
Bhardwaj Hem Shruti,
Ramireddy Thrinathreddy,
Pradeep Anagha,
Jangid Manoj K.,
Srihari Velaga,
Poswal Himanshu K.,
Mukhopadhyay Amartya
Publication year - 2018
Publication title -
chemelectrochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.182
H-Index - 59
ISSN - 2196-0216
DOI - 10.1002/celc.201701276
Subject(s) - materials science , electrochemistry , anode , electrolyte , phase (matter) , diffusion , ion , chemical engineering , analytical chemistry (journal) , electrode , chemistry , thermodynamics , physics , organic chemistry , chromatography , engineering
Despite being a promising anode material for the Na‐ion battery system, Na‐titanate ( viz ., Na 2 Ti 3 O 7 ) lacks in terms of cyclic stability; the cause(s) for which are under debate. Against this backdrop, through electrochemical measurements and in situ synchrotron X‐ray diffraction studies, the present work develops insights into the aspects concerning electrochemical reversibility of the fully sodiated phase ( i.e ., Na 4 Ti 3 O 7 ), possible occurrence of irreversible reactions in Na‐ion cells, influences of the same towards cyclic instability, and a strategy towards alleviating this problem. The in situ studies rule out (in)stability/(ir)reversibility of Na 4 Ti 3 O 7 as being a major cause for the capacity fade; rather they indicate the formation of ‘impurity’ phase(s) due to reaction with the electrolyte. Incorporation of multi‐walled carbon nanotubes (MWCNTs; uniformly ‘wrapping’ the rod‐shaped Na 2 Ti 3 O 7 particles) significantly improved the cyclic stability (ca. 78 % reversible capacity retention after 50 cycles, as compared to ca. 6 % without MWCNTs) and rate capability (with nearly flat potential plateaus at 5C). The same suppressed the increase in charge‐transfer resistance upon cycling by an order of magnitude and also changed the sodiation reaction from being primarily surface to diffusion controlled. Correlation of the results/analysis indicate that, in the absence of a stable conducting network, loss in electrical connectivity owing to the formation of insulating/passivating (surface) phase(s) is the major cause for capacity fade of Na 2 Ti 3 O 7 .